Dual cure resins for additive manufacturing

ABSTRACT

Provided herein is a resin product useful for the production of three-dimensional objects by additive manufacturing, and methods using the same. The resin may include a reactive blocked prepolymer comprising a prepolymer blocked with reactive blocking groups; a polyol; a photoinitiator; and at least one organometallic catalyst. A packaged product useful for the production of three-dimensional objects by additive manufacturing, the product comprising a single container having a single chamber and a resin in the chamber with all components mixed together, is also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/276,858, filed Mar. 17, 2021, now allowed, which is a 35 U.S.C. § 371national phase application of International Application Ser. No.PCT/US2019/052553, filed Sep. 24, 2019, which claims priority to U.S.Provisional Application Ser. Nos. 62/735,987 and 62/858,687, filed Sep.25, 2018, and Jun. 7, 2019, respectively, the entire contents of whichare hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention concerns additive manufacturing in general, andparticularly concerns dual cure resins suitable for bottom-up ortop-down stereolithography.

BACKGROUND OF THE INVENTION

In conventional additive manufacturing techniques (often referred to as“3D printing”), construction of a three-dimensional object is performedin a step-wise or layer-by-layer manner by sequentially exposing alight-polymerizable resin to patterned light. Generally referred to as“stereolithography,” numerous examples are known, including thosedescribed in U.S. Pat. No. 5,236,637 to Hull (see, e.g., FIGS. 3-4) andU.S. Pat. No. 7,892,474 to Shkolnik. Additional examples are given inU.S. Pat. Nos. 5,391,072 and 5,529,473 to Lawton, U.S. Pat. No.7,438,846to John, U.S. Pat. No. 8,110,135 to El-Siblani, and U.S. PatentApplication Publication Nos. 2013/0292862 to Joyce and 2013/0295212 toChen et al.

Unfortunately, additive manufacturing techniques have generally beenslow, and have long been known to produce parts with a limited range ofmechanical properties, frequently rendering such products unsuitable forreal world use beyond simple prototyping.

Techniques referred to as “continuous liquid interface production” (or“CLIP”) have been developed more recently. These techniques enable therapid production of three-dimensional objects, preferably in a layerlessmanner, by which the parts may have desirable structural and mechanicalproperties. See, e.g., J. DeSimone et al., U.S. Pat. Nos. 9,211,678;9,205,601; and 9,216,546; J. Tumbleston, et al., Continuous liquidinterface production of 3D Objects, Science 347, 1349-1352 (2015), andR. Janusziewcz et al., Layerless fabrication with continuous liquidinterface production, Proc. Natl. Acad. Sci. USA 113, 11703-11708(2016).

More recently, dual cure stereolithography resins suitable forstereolithography techniques (particularly for CLIP) are described in J.Rolland et al., U.S. Pat. No. 9,453,142, 9,676,963, and 9,598,606, andUS Patent Application Publication No. 2016/0160077. These resins usuallyinclude a first polymerizable component typically polymerized by light(sometimes referred to as “Part A”) from which an intermediate object isproduced, and also include at least a second polymerizable component(“Part B”) which is usually cured after the intermediate object is firstformed, and which imparts desirable structural and/or tensile propertiesto the final object.

These two developments have spurred the application of additivemanufacturing processes beyond the manufacture of (primarily) prototypeobjects, to functional objects more suited to a variety of end uses.This has spurred the need for new resin formulations which have goodperformance characteristics during additive manufacturing, producefinished objects with satisfactory tensile characteristics, havereasonable storage stability, and are suitable for convenient forms ofpackaging and dispensing.

SUMMARY OF THE INVENTION

A first aspect of the present invention is a resin product useful forthe production of three-dimensional objects by additive manufacturing,the resin including: (a) a reactive blocked prepolymer comprising aprepolymer blocked with reactive blocking groups; (b) a polyol (e.g., adiol, a triol, etc., including combinations thereof); (c) aphotoinitiator; and (d) at least one organometallic catalyst.

In some embodiments, the resin comprises: (a) a reactive blockedprepolymer comprising a prepolymer blocked with reactive blocking groups(e.g., in an amount of from 5 to 90 percent by weight); (b) a polyol(e.g., a diol or triol) (e.g., in an amount of from 5 to 30 or 40percent by weight); (c) a photoinitiator (e.g., a free radicalphotoinitiator) (e.g., in an amunt of from 0.1 to 4 percent by weight);(d) at least one organometallic catalyst (e.g., in a total amount offrom 0.01, 0.05, 0.1, 0.2, or 0.3 percent by weight to 1, 2 or 3 percentby weight); (e) optionally, but in some embodiments preferably, areactive diluent (e.g., in an amount of from 1 or 5 percent by weight to40 or 50 percent by weight); (f) optionally, but in some embodimentspreferably, a filler (e.g., in an amount of from 1, 2, 5 or 10 percentby weight to 50 percent by weight); and (g) optionally, but in someembodiments preferably, a pigment or dye (e.g., in an amount of from0.05, 0.1 or 0.5 percent by weight to 2, 4 or 6 percent by weight).

In some embodiments, the prepolymer comprises a polyurethane prepolymer,a polyurea prepolymer, a polyurethane-polyurea copolymer, or acombination thereof. In some embodiments, the reactive blockedprepolymer comprises reactive end groups selected from the groupconsisting of acrylates, methacrylates, alpha-olefins, N-vinyls,acrylamides, methacrylamides, styrenics, epoxides, thiols, 1,3-dienes,vinyl halides, acrylonitriles, vinyl esters, maleimides, and vinylethers.

In some embodiments, the reactive blocking group comprises an amine(meth)acrylate monomer blocking agent (e.g., tertiary-butylaminoethylmethacrylate (TBAEMA), tertiary pentylaminoethyl methacrylate (TPAEMA),tertiary hexylaminoethyl methacrylate (THAEMA),tertiary-butylaminopropyl methacrylate (TBAPMA),tertiary-octylaminoethyl methacrylate (TOAEMA), acrylate analogsthereof, and mixtures thereof).

In some embodiments, the reactive blocked prepolymer comprises a(meth)acrylate-blocked prepolymer.

In some embodiments, the reactive blocked prepolymer is blocked with avinyl amide blocking agent such as N-vinylformamide (NVF) orN-vinylacetamide (NVA).

In some embodiments, the reactive blocked prepolymer comprises a vinylamide blocked polyisocyanate such as an N-vinylformamide blockedpolyisocyante. In some embodiments, the reactive diluent is present andmay include an acrylate, a methacrylate, a styrene, a vinylamide, avinyl ether, a vinyl ester, polymers containing any one or more of theforegoing, and combinations with one or more of the foregoing (e.g.,acrylonitrile, styrene, divinyl benzene, vinyl toluene, methyl acrylate,ethyl acrylate, butyl acrylate, a fatty alcohol (meth)acrylate such aslauryl acrylate, isobornyl acrylate (IBOA), isobornyl methacrylate(IBOMA), an alkyl ether of mono-, di- or triethylene glycol acrylate ormethacrylate, a fatty alcohol acrylate or methacrylate such as lauryl(meth)acrylate, and mixtures thereof).

In some embodiments, the organometallic catalyst comprising: a metalamidine complex and/or a second compound, wherein the second compound isa metal carboxylate or a carboxylic acid, and/or a third compoundwherein the third compound is a metal chelate complex of anacetylacetonate (e.g., pentanedione), optionally wherein the metal ofthe metal amidine complex and the metal of the metal carboxylate and/orthe metal of the metal acetylacetonate (when present) are not identical.In some embodiments, the metal amidine complex is of the chemicalformula metal(amidine)_(w)(carboxylate)₂, wherein w is an integer from 1to 4. In some embodiments, the metal of the metal amidine complex, themetal of the metal carboxylate, and the metal of the chelate complex areindependently copper, zinc, lithium, sodium, magnesium, barium,potassium, calcium, bismuth, cadmium, aluminum, zirconium, tin, hafnium,titanium, lanthanum, vanadium, niobium, tantalum, tellurium, molybdenum,tungsten, or cesium. In some embodiments, the metal of the metal amidinecomplex and the metal of the metal carboxylate are independently zinc orbismuth. In some embodiments, the amidine is 1,1,3,3-tetramethylguanidine or 1-methylimidazole. In some embodiments, the chelate ispentanedione, hexafluoropentanedione or tetramethyloctanedione. In someembodiments, the carboxylate is octoate, neodecanoate, naphthenate,stearate, or oxalate. In some embodiments, the second compound comprisesa zinc carboxylate and/or a bismuth carboxylate.

A second aspect of the invention is a packaged product useful for theproduction of three-dimensional objects by additive manufacturing, theproduct comprising a single container having a single chamber and aresin in the chamber, the resin comprising a resin as described herein,with all components mixed together (i.e., a “1K resin”).

A further aspect of the invention is a method of making athree-dimensional object, comprising: dispensing a resin as describedherein (which may be from a packaged produce as described herein) intoan additive manufacturing apparatus (e.g., a bottom-up or top-downstereolithography apparatus); producing an intermediate object from theresin by photopolymerization in the additive manufacturing apparatus;and then heating and/or microwave irradiating the intermediate object tofurther polymerize said resin and form said three-dimensional object.

In some embodiments, the producing is carried out by photopolymerizingsaid reactive blocked prepolymer to form a polymer scaffold carryingsaid polyol; and said heating and/or microwave irradiating is carriedout under conditions in which said polymer scaffold at least partiallydegrades and regenerates said prepolymer, said prepolymer in turnpolymerizing with said polyol to form said three-dimensional object.

The foregoing and other objects and aspects of the present invention areexplained in greater detail in the specification set forth below. Thedisclosures of all United States patent references cited herein are tobe incorporated herein by reference to the extent consistent with thepresent disclosure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention is now described more fully hereinafter withreference to embodiments. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather these embodiments are provided sothat this disclosure will be thorough and complete and will fully conveythe scope of the invention to those skilled in the art.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises” or“comprising,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements components and/orgroups or combinations thereof, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components and/or groups or combinations thereof. The sequenceof operations (or steps) is not limited to the order presented in theclaims or figures unless specifically indicated otherwise.

As used herein, the term “and/or” includes any and all possiblecombinations or one or more of the associated listed items, as well asthe lack of combinations when interpreted in the alternative (“or”).

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the specification andclaims and should not be interpreted in an idealized or overly formalsense unless expressly so defined herein. Well-known functions orconstructions may not be described in detail for brevity and/or clarity.

It will be understood that, although the terms first, second, etc., maybe used herein to describe various elements, components, regions, layersand/or sections, these elements, components, regions, layers and/orsections should not be limited by these terms. Rather, these terms areonly used to distinguish one element, component, region, layer and/orsection, from another element, component, region, layer and/or section.Thus, a first element, component, region, layer or section discussedherein could be termed a second element, component, region, layer orsection without departing from the teachings of the present invention.

1. Catalysts.

In the present invention, one or more metal organometallic chelatecatalysts, such as non-tin catalysts, are advantageously incorporatedinto the resin composition. Such catalysts are known and described in,for example, U.S. Pat. No. 5,965,686 to Blank et al., U.S. Pat. No.8,912,113 to Ravichandran et al.; U.S. Pat. No. 9,066,316 to Hsieh etal., and U.S. Pat. No. 10,023,764 to Hsieh et al.; and in W. Blank etal., Catalysis of the Isocyanate-Hydroxyl Reaction by Non-Tin Catalysts(1999); W. Blank et al., Catalysis of Blocked Isocyanates with Non-TinCatalysts (2000); J. Florio et al., Novel Bismuth Carboxylate Catalystswith Good Hydrolytic Stability and HFO Compatibility (2017); thedisclosures of which are incorporated herein by reference in theirentirety.

In some embodiments, the organometallic catalyst comprises: a metalamidine complex and/or a second compound, wherein the second compound isa metal carboxylate or a carboxylic acid, and/or a third compoundwherein the third compound is a metal chelate complex of anacetylacetonate (e.g., pentanedione), optionally wherein the metal ofthe metal amidine complex and the metal of the metal carboxylate and/orthe metal of the metal acetylacetonate (when present) are not identical.Note that the various organic groups can be substituted orunsubstituted. For example, the acetylacetonate can he furthersubstituted, for instance with one to six methyl groups or one to sixfluorines at the 1 and 5 positions,

In some embodiments, the metal amidine complex is of the chemicalformula metal(amidine)_(w)(carboxylate)₂, wherein w is an integer from 1to 4.

In some embodiments, the metal of the metal amidine complex, the metalof the metal carboxylate, and the metal of the chelate complex areindependently copper, zinc, lithium, sodium, magnesium, barium,potassium, calcium, bismuth, cadmium, aluminum, zirconium, tin, hafnium,titanium, lanthanum, vanadium, niobium, tantalum, tellurium, molybdenum,tungsten, or cesium.

In some embodiments, the metal of the metal amidine complex and themetal of the metal carboxylate are independently zinc or bismuth.

In some embodiments, the amidine is 1,1,3,3-tetramethyl guanidine or1-methylimidazole.

In some embodiments, the chelate is pentanedione, hexafluoropentanedioneor tetramethyloctanedione.

In some embodiments, the carboxylate is octoate, neodecanoate,naphthenate, stearate, or oxalate.

In some embodiments, the second compound comprises a zinc carboxylateand/or a bismuth carboxylate.

Particular examples of suitable catalysts include, but are not limitedto K-KAT® catalysts 4205, XK-348, XK-635, XK-651, XK-661, XK-672, andXK-678, available from KingIndustries, 1 Science Road, Norwalk, Conn.06852 USA (See generally King Industries, K-KAT® Guide to Tin-FreeCatalysts for Urethane Coatings (2018)).

2. Resins.

In addition to the catalysts described above, additional constituentsfor a dual cure resin of the present invention are described in, forexample, U.S. Pat. Nos. 9,453,142; 9,598,606; 9,676,963; and 9,982,164to Rolland et al, the disclosures of which are incorporated herein byreference.

In general, a resin of the present invention may include:

(a) a reactive blocked prepolymer comprising a prepolymer blocked withreactive blocking groups (e.g., in an amount of from 5 to 90 percent byweight);

(b) a polyol (e.g., a diol, a triol, etc., including combinationsthereof) (e.g., in an amount of from 5 to 30 or 40 percent by weight);

(c) a photoinitiator (e.g., a free radical photoinitiator) (e.g., in anamount of from 0.1 to 4 percent by weight);

(d) at least one organometallic catalyst (e.g., in a total amount offrom 0.01, 0.05, 0.1, 0.2, or 0.3 percent by weight to 1, 2 or 3 percentby weight);

(e) optionally, but in some embodiments preferably, a reactive diluent(e.g., in an amount of from 1 or 5 percent by weight to 40 or 50 percentby weight);

(f) optionally, but in some embodiments preferably, a filler (e.g., inan amount of from 1, 2, 5 or 10 percent by weight to 50 percent byweight); and

(g) optionally, but in some embodiments preferably, a pigment or dye(e.g., in an amount of from 0.05, 0.1 or 0.5 percent by weight to 2, 4or 6 percent by weight).

In some embodiments, the prepolymer comprises a polyurethane prepolymer,a polyurea prepolymer, a polyurethane-polyurea copolymer, or acombination thereof.

In some embodiments, the reactive blocked prepolymer comprises reactiveend groups selected from the group consisting of acrylates,methacrylates, alpha-olefins, N-vinyls, acrylamides, methacrylamides,styrenics, epoxides, thiols, 1,3-dienes, vinyl halides, acrylonitriles,vinyl esters, maleimides, and vinyl ethers.

In some embodiments, the reactive blocking group comprises an amine(meth)acrylate monomer blocking agent (e.g., tertiary-butylaminoethylmethacrylate (TBAEMA), tertiary pentylaminoethyl methacrylate (TPAEMA),tertiary hexylaminoethyl methacrylate (THAEMA),tertiary-butylaminopropyl methacrylate (TBAPMA),tertiary-octylaminoethyl methacrylate (TOAEMA), acrylate analogsthereof, and mixtures thereof).

In some embodiments, the reactive blocking group comprises a vinyl amideblocking agent such as N-vinylformamide (NVF) or N-vinylacetamide (NVA).

In some embodiments, the reactive blocked prepolymer comprises a(meth)acrylate-blocked prepolymer. In some embodiments, the reactiveblocked prepolymer comprises a vinylamide blocked polyisocyanate.

In some embodiments, the prepolymer comprises blocked polyisocyanates.Polyisocyanates (including diisocyanates) useful in carrying out thepresent invention include, but are not limited to,1,1′-methylenebis(4-isocyanatobenzene) (MDI),2,4-diisocyanato-1-methylbenzene (TDI),methylene-bis(4-cyclohexylisocyanate) (H12MDI), hexamethylenediisocyanate (HDI), isophorone diisocyanate (IPDI), 2,2,4-(2,4,4-)trimethylhexane 1,6-diisocyantate (TMHDI, e.g., VESTANAT® TMDI,available from Evonik (Essen, Germany)), polymeric MDI, 1,4-phenylenediisocyanate (PPDI), and o-tolidine diisocyanate (TODI). A preferreddiisocyanate in some embodiments is H12MDI, such as Desmodur® W,supplied by Covestro AG (Leverkusen, Germany). Additional examplesinclude but are not limited to those given in U.S. Pat. No. 3,694,389 toLevy.

Examples of diol or polyol (e.g., triol) chain extenders include, butare not limited to, ethylene glycol, diethylene glycol, triethyleneglycol, tetraethylene glycol, propylene glycol, dipropylene glycol,tripropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol,neopentyl glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol,hydroquinone bis(2-hydroxyethyl) ether (HQEE), glycerol,trimethylolpropane, 1,2,6-hexanetriol, and pentaerythritol. Natural oilpolyols (biopolyols) may also be used. Such polyols may be derived,e.g., from vegetable oils (triglycerides), such as soybean oil, by knowntechniques. See, e.g., U.S. Pat. No. 6,433,121 to Petrovic et al.Alkoxylates such as ethoxylates, propoxylates, butoxylates, etc., ofdiols, triols and higher polyalcohols may also be used, for instance,trimethylolpropane ethoxylate Mn=450 (TPE), which in some embodiments ispreferred.

In some embodiments, the reactive diluent comprises an acrylate, amethacrylate, a styrene, a vinylamide, a vinyl ether, a vinyl ester,polymers containing any one or more of the foregoing, or a combinationof one or more of the foregoing (e.g., acrylonitrile, styrene, divinylbenzene, vinyl toluene, methyl acrylate, ethyl acrylate, butyl acrylate,methyl (meth)acrylate, isobornyl acrylate (IBOA), isobornyl methacrylate(IBOMA), 4-t-butyl-cyclohexyl (meth)acrylate, cyclic trimethylolpropaneformal (meth)acrylate, 3,3,5 -trimethylcyclohexyl (meth)acrylate,tricyclodecane dimethanol di(meth)acrylate, an alkyl ether of mono-, di-or triethylene glycol acrylate or methacrylate, a fatty alcohol acrylateor methacrylate such as lauryl (meth)acrylate, and mixtures thereof).

Photoinitiators included in the polymerizable liquid (resin) can be anysuitable photoiniator, including type I and type II photoinitiators andincluding commonly used UV photoinitiators, examples of which includebut are not limited to acetophenones (diethoxyacetophenone for example),phosphine oxides such as diphenyl(2,4,6-trimethylbenzoyl)phosphineoxide, phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide (PPO),Irgacure® 369, etc. See, e.g., U.S. Pat. No. 9,453,142 to Rolland et al.The liquid resin can have solid particles suspended or dispersedtherein. Any suitable solid particle can be used, depending upon the endproduct being fabricated. The particles can be metallic,organic/polymeric, inorganic, or composites or mixtures thereof. Theparticles can be nonconductive, semi-conductive, or conductive(including metallic and non-metallic or polymer conductors); and theparticles can be magnetic, ferromagnetic, paramagnetic, or nonmagnetic.The particles can be of any suitable shape, including spherical,elliptical, cylindrical, etc. The particles can be of any suitable size(for example, ranging from 1 nm to 20 μm average diameter).

The particles can comprise an active agent or detectable compound asdescribed below, though these may also be provided dissolved orsolubilized in the liquid resin as also discussed below. For example,magnetic or paramagnetic particles or nanoparticles can be employed.

The liquid resin can have additional ingredients solubilized therein,including pigments, dyes, diluents, active compounds or pharmaceuticalcompounds, detectable compounds (e.g., fluorescent, phosphorescent,radioactive), etc., again depending upon the particular purpose of theproduct being fabricated. Examples of such additional ingredientsinclude, but are not limited to, proteins, peptides, nucleic acids (DNA,RNA) such as siRNA, sugars, small organic compounds (drugs and drug-likecompounds), etc., including combinations thereof.

Dyes/non-reactive light absorbers. In some embodiments, resins forcarrying out the present invention include a non-reactive pigment or dyethat absorbs light, particularly UV light. Suitable examples of suchlight absorbers include, but are not limited to: (i) titanium dioxide(e.g., included in an amount of from 0.05 or 0.1 to 1 or 5 percent byweight), (ii) carbon black (e.g., included in an amount of from 0.05 or0.1 to 1 or 5 percent by weight), and/or (iii) an organic ultravioletlight absorber such as a hydroxybenzophenone,hydroxyphenylbenzotriazole, oxanilide, benzophenone, thioxanthone,hydroxyphenyltriazine, and/or benzotriazole ultraviolet light absorber(e.g., Mayzo BLS1326) (e.g., included in an amount of 0.001 or 0.005 to1, 2 or 4 percent by weight). Examples of suitable organic ultravioletlight absorbers include, but are not limited to, those described in U.S.Pat. Nos. 3,213,058; 6,916,867; 7,157,586; and 7,695,643, thedisclosures of which are incorporated herein by reference.

Fillers. Any suitable filler may be used in connection with the presentinvention, depending on the properties desired in the part or object tobe made. Thus, fillers may be solid or liquid, organic or inorganic, andmay include reactive and non-reactive rubbers, siloxanes,acrylonitrile-butadiene rubbers, reactive and non-reactivethermoplastics (including but not limited to: poly(ether imides),maleimide-styrene terpolymers, polyarylates, polysulfones andpolyethersulfones, etc.) inorganic fillers such as silicates (such astalc, clays, silica, mica), glass, carbon nanotubes, graphene, cellulosenanocrystals, etc., including combinations of all of the foregoing.Suitable fillers include tougheners, such as core-shell rubbers, asdiscussed below.

Tougheners. One or more polymeric and/or inorganic tougheners can beused as a filler in the present invention. The toughener may beuniformly distributed in the form of particles in the cured product. Theparticles could be less than 5 microns (μm) in diameter. Such toughenersinclude, but are not limited to, those formed from elastomers, branchedpolymers, hyperbranched polymers, dendrimers, rubbery polymers, rubberycopolymers, block copolymers, core-shell particles, oxides or inorganicmaterials such as clay, polyhedral oligomeric silsesquioxanes (POSS),carbonaceous materials (e.g., carbon black, carbon nanotubes, carbonnanofibers, fullerenes), ceramics and silicon carbides, with or withoutsurface modification or functionalization.

Core-shell rubbers. Core-shell rubbers are particulate materials(particles) having a rubbery core. Such materials are known anddescribed in, for example, US Patent Application Publication No.20150184039, as well as US Patent Application Publication No.20150240113, and U.S. Pat. Nos. 6,861,475, 7,625,977, 7,642,316,8,088,245, and elsewhere. In some embodiments, the core-shell rubberparticles are nanoparticles (i.e., having an average particle size ofless than 1000 nanometers (nm)). Generally, the average particle size ofthe core-shell rubber nanoparticles is less than 500 nm, e.g., less than300 nm, less than 200 nm, less than 100 nm, or even less than 50 nm.Typically, such particles are spherical, so the particle size is thediameter; however, if the particles are not spherical, the particle sizeis defined as the longest dimension of the particle. Suitable core-shellrubbers include, but are not limited to, those sold by KanekaCorporation under the designation Kaneka Kane Ace, including the KanekaKane Ace 15 and 120 series of products, including Kaneka Kane Ace MX120, Kaneka Kane Ace MX 153, Kaneka Kane Ace MX 154, Kaneka Kane Ace MX156, Kaneka Kane Ace MX170, Kaneka Kane Ace MX 257 and Kaneka Kane AceMX 120 core-shell rubber dispersions, and mixtures thereof.

Organic diluents. In some embodiments, diluents for use in the presentinvention are preferably reactive organic diluents; that is, diluentsthat will degrade, isomerize, cross-react, or polymerize, withthemselves or a light polymerizable component, during the additivemanufacturing step. In general, the diluent(s) are included in an amountsufficient to reduce the viscosity of the polymerizable liquid or resin(e.g., to not more than 15,000, 10,000, 6,000, 5,000, 4,000, or 3,000centipoise at 25 degrees Centigrade). Suitable examples of diluentsinclude, but are not limited to, isobornyl methacrylate, TBAEMA(tert-butyl amino ethyl methacrylate), tetrahydrofurfuryl methacrylate,N,N-dimethylacrylamide, N-vinyl-2-pyrrolidone, N-vinylformamide, andMichael adducts of N-vinylformamide with (meth)acrylates (known anddescribed in, for example, U.S. Pat. No. 5,672,731 to Chen et al.), or amixture if two or more thereof. The diluent may be included in thepolymerizable liquid in any suitable amount, typically from 1, 5 or 10percent by weight, up to about 30 or 40 percent by weight, or more.

Resin packaging. As noted above, the resin may be packaged as twoseparate precursors, which are mixed together and dispensed prior to use(sometimes referred to as “2K resins”) or may be packaged in a premixedform, in the same chamber of a single container (sometimes referred toas a “1K” resin). In either case, the resin is dispensed into anadditive manufacturing apparatus for production of a “green”intermediate object, as discussed further below.

3. Use in additive manufacturing.

Techniques for additive manufacturing are known. Suitable techniquesinclude bottom-up or top-down additive manufacturing, generally known asstereolithography. Such methods are known and described in, for example,U.S. Pat. No. 5,236,637 to Hull, U.S. Pat. Nos. 5,391,072 and 5,529,473to Lawton, U.S. Pat. No. 7,438,846 to John, U.S. Pat. No. 7,892,474 toShkolnik, U.S. Pat. No. 8,110,135 to El-Siblani, U.S. Patent ApplicationPublication No. 2013/0292862 to Joyce, and US Patent ApplicationPublication No. 2013/0295212 to Chen et al. The disclosures of thesepatents and applications are incorporated by reference herein in theirentirety.

In some embodiments, the object is formed by continuous liquid interfaceproduction (CLIP). CLIP is known and described in, for example, U.S.Pat. Nos. 9,211,678, 9,205,601, 9,216,546, and in J. Tumbleston, D.Shirvanyants, N. Ermoshkin et al., Continuous liquid interfaceproduction of 3D Objects, Science 347, 1349-1352 (2015). See also R.Janusziewcz et al., Layerless fabrication with continuous liquidinterface production, Proc. Natl. Acad. Sci. USA 113, 11703-11708(2016). Other examples of methods and apparatus for carrying outparticular embodiments of CLIP include, but are not limited to, thoseset forth in: B. Feller, US Patent App. Pub. No. US 2018/0243976(published Aug. 30, 2018); M. Panzer and J. Tumbleston, US Patent AppPub. No. US 2018/0126630 (published May 10, 2018); K. Willis and B.Adzima, US Patent App Pub. No. US 2018/0290374 (Oct. 11, 2018);Batchelder et al., Continuous liquid interface production system withviscosity pump, US Patent Application Pub. No. US 2017/0129169; Sun andLichkus, Three-dimensional fabricating system for rapidly producingobjects, US Patent Application Pub. No. US 2016/0288376; Willis et al.,3d print adhesion reduction during cure process, US Patent ApplicationPub. No. US 2015/0360419; Lin et al., Intelligent 3d printing throughoptimization of 3d print parameters, US Patent Application Pub. No. US2015/0331402; and D. Castanon, Stereolithography System, US PatentApplication Pub. No. US 2017/0129167.

As noted above, in the present invention, a resin as described above isdispensed into an additive manufacturing apparatus (e.g., a bottom-up ortop-down stereolithography apparatus), and an intermediate objectproduced in the apparatus by photopolymerization. The intermediateobject is optionally cleaned (e.g., by washing), and then heated and/ormicrowave irradiated to further polymerize the resin and form thethree-dimensional object. In general, the producing step is carried outby photopolymerizing the reactive blocked prepolymer to form a polymerscaffold carrying a polyol; and the heating and/or microwave irradiatingstep is carried out under conditions in which said polymer scaffold atleast partially degrades and generates a reactive prepolymer, saidprepolymer in turn polymerizing with said polyol to form saidthree-dimensional object. See generally U.S. Pat. Nos. 9,453,142;9,598,606; 9,676,963; and 9,982,164 to Rolland et al., the disclosuresof which are incorporated herein by reference.

The present invention is further described in the following non-limitingexamples.

EXAMPLES

Example 1: Alcohol cure of AmBPU. Use of a diol or triol curative withamide (NVF) blocked diisocyanate overcomes the rapid side reaction thatcan occur with an amine curative. Printed dog bones show desirableelastomer properties after 160 ° C. post-cure.

An amide-blocked polyurethane (AmBPU) was formed in whichN-vinylformamide (NVF) replaces sterically hindered amine t-BAEMA(Scheme 1).

Use of a triamine curative rapidly degraded the vinylimide at roomtemperature. Switching to an alcohol curative, trimethylolpropaneethoxylate (TPE), and adding Kkat 348 urethane catalyst gave a morestable formulation. The NVF-tBAEMA-HDI-PTMO650 AmBPU [1/0.05/1/1] wasdiluted with isobornyl acrylate (IBOA) to provide a small excess ofacrylate and printed, using RPU70 (methacrylate) settings forconvenience. The resulting dog bones with faster reactingvinylimide-acrylate were somewhat oversized (normal width/thickness˜3.18/3.98 mm).

Post-cure at 120° C. (12 hr) or 160° C. (4 hr) reduced stickiness(especially in the latter case) and dramatically improved elasticity andtensile performance, as shown in Table 1. Cure at 160 ° C. showed over300% elongations.

These results demonstrate the viability of using NVF as a tBAEMAreplacement in alcohol post-cured engineering resins.

TABLE 1 Material Properties Ultimate Tensile Elong @ NVF Thick- TensileStrength Yld AmBPU + Width ness Strength at Yield (mm/ TPE (mm) (mm)Modulus (MPa) (MPa) mm) green 3.9 4.5 0.91 2.96 2.88 0.57 12 hr 120° C.3.9 4.5 0.61 2.86 2.79 1.4 4 hr 160° C. 3.43 3.806 1.96 7.52 7.52 3.24

Example 2: N-vinylacetamide (NVA) based AmBPU. More stable, but slightlymore hindered N-vinylacetamide reacted unusably slowly withhexanediisocyanate. NVA is generally more stable than NVF, offers adifferent T_(g), and is commercially available (Showa Denko K. K.,Tokyo, Japan). Conversion to a final AmBPU under conditions used withNVF, however, was slow. Temperatures of 81° C. with both Zr and Bicatalysts at 0.5% levels achieved only 50% apparent conversion over sixhours. P. Kurtz and H. Disselnkoetter, Liebigs Ann. Chem., 764, 69(1972) have reported that only NVF was reactive with isocyanates.

Example 3: Formation of an NVF blocked polyurethane (AmBPU). A 500 mLround bottom three neck flask with mechanical stirrer, dry air feed,addition funnel, thermocouple, and heating bath was charged with 0.5mole of hexanediisocyanate (HDI), 500 ppm each of MEHQ anddi-t-butylated hydroxytoluene (BHT), 2.35 g King Industries K-KAT® 4205urethane catalyst (1%), and 0.25 mole of N-vinylformamide (NVF). Thesample was heated to 78° C. while stirring. The reaction beganexotherming at around 65° C. and stabilized after 10 min. A second 0.25mole of NVF was added and the temperature was maintained at 74-76° C.until tic showed essentially complete NVF consumption (2hr 15 min).Poly(tetramethyleneoxide), (PTMO), MW 650, 0.259 mole was added slowlywith a rapid temperature rise to 88° C. After 30 min the exotherm wascomplete. Tetraethylene glycol (0.01 equivalent) was added and areaction sample titrated for zero NCO (confirmed by IR). An additional74 mg of BHT was added and the reaction was terminated. NMR showed >85%conversion of NVF.

Example 4: CLIP Printing of AmBPU. 50.4 g of the resin of Example 3 wascombined with 22.3 g of isobornyl acrylate, 12.24 g oftrimethylolpropane ethoxylate (TPE, MW 450), 1.27 g of TPO-Lphotoinitiator, and 0.086 g of BLS1326 light stabilizer. This wasthoroughly mixed on a Thinky mixer and 15 dog bones were printed on aCarbon M1 printer (Carbon Inc., Redwood City, Calif.). Dog bones werepost-cured at different temperatures and Instron tensiles were pulledwith the results shown in the Table 2.

TABLE 2 Tensile NVF AmBPU + Modulus Tensile stress @ IBOA + TPE (has(Auto strain Break # 1% Kkat 4205) Young's) (mm/mm) (Mpa) Repeats 1.5%TPO-L + 10.7 0.57 3.04 5 0.1% BLS1326, Green 120° C./4 hr 11.7 0.55 2.785 140° C./6 hr 6.11 1.4 2.81 5 160° C./4 hr 8.19 3.1 4.87 4

The modulus and tensile stress declined somewhat and the elongationimproved dramatically as polyurethane networks formed on reaction withthe triol curative.

Example 5: Triamine versus Triol Cure of ABPU. Part A of commercial 3Dprinting resin RPU70 (Carbon Inc., Redwood City, Calif.), which containst-butylaminoethyl methacrylate blocked ABPUs, in control runs wascombined through an in-line mixer with

Huntsman triamine curative, T403, MW 440, in a ratio to react with theblocked isocyanate groups and 3D printed within 1 to 24 hrs. The printeddog bone samples were then post-cured in an oven, for 8 to 12 hrs at120° C. Tensiles were then pulled on an Instron.

RPU70 Part A was separately mixed (Thinky mixer) with a stoichiometricamount of triol, trimethylolpropane ethoxylate (TPE, MW 450), and aurethane catalyst (K-KAT® XK-651, King Industries, Norwalk,Connecticut). Samples were then printed and cured as above, but withdifferent cure times and temperatures, and evaluated by Instron testing.

Table 3 below compares Instron tensile performance for RPU70 Part Acured with the triamine and the triol curatives, with and withoutthermal post-cure. Note that the Modulus and tensile stress at breakdecline somewhat, but the tensile strain increases significantly uponthermal cure, reflecting a significant and desirable increase inflexibility and toughness.

TABLE 3 Triamine vs. Triol Cure Modulus Tensile (Auto Tensile stress @Young's, strain Break # RPU70A + MPa) (mm/mm) (MPa) Repeats T403triamine, Green 1616.5 0.04 40.7 4 T403 6 hr 120° C. cure 1395.4 0.3829.2 6 TPE + 0.5% K651, Green 595.3 0.51 17.9 4 4 hr 120° C. cure 813.70.63 27.2 5 2 hr 120° C. + 1 hr 140° C. 804.9 0.54 26.7 5

Example 6: Evaluation of Viscosity Rise in ABPU Resin Formulations. As afaster method to evaluate cure of amine blocked polyurethanes, viscosityrise of a small sample was measured upon heating on a parallel platerheometer. Samples of RPU70 Part A were hydrogenated in ethyl acetate atroom temperature and 165 psi with Pd on carbon catalyst for 12-24 hr tosuppress viscosity rise from thermal free radical reaction. Afterremoval of solvent, small samples were mixed as above and about 14microliter samples were placed under an 8 mm Al parallel plate on a TAInstruments Discovery rheometer in oscillation mode and heated withmeasurement of initial viscosity and G′ (viscosity) vs. time andtemperature.

Hydrogenated RPU70 Part A (HRPU70A) samples without curative or withonly triol curative gave little or no viscosity rise up to 160 ° C., asreflected in Table 4. By contrast, addition of T403 triamine resulted ina rise in viscosity at 120° C. after about 45 minutes. There was noviscosity rise/cure with no curative, or with triol (triethanolamine(TEOA) or TPE) without catalyst.

There was also no triol cure under these conditions with known tertiaryamine urethane catalysts (DMCHA, TBD), but strong, effective cure withmetallic urethane catalysts. The speed of cure (time and temperature ofcure onset) also increased with metal catalyst concentration. Note thatin the last example a mix of tertiary amine and metal catalyst was notas effective.

TABLE 4 Cure of Hydrogenated RPU70A with triol and catalyst InitialInitial Rise Rise temp Time Resin Curative Catalyst (° C.) (sec) FinalG′ Control none none 120 1700 >10⁵ RPU70 HRPU70 none none none no rise<10³ HRPU70A T403 none 120 2700 >10⁵ HRPU70A TEOA none none no rise <10³triol HRPU70A TPE triol DMCHA* >160 >3000 no cure HRPU70A TPE triol0.25% K651 120 900 >10⁵ HRPU70A TPE triol 1.0% K651 140 380 8 × 10⁴HRPU70A TPE triol 2.5% K651 120 500 3 × 10⁴ HRPU70A TPE triol 1%TBD* >160 >3000 no cure HRPU70A TPE triol 2.5% K651 + 180 100 small, 1%DMCHA slow rise *DMCHA = N,N-dimethylcyclohexylamine, TBD =triazabicyclodecene

Example 7: Catalyst Seletion and Cure Speed. Table 5 below shows thatcatalyst selection impacts cure speed.

TABLE 5 Cure of RPU70A + TPE vs. Catalyst (1%). Rise Rise Sample tempTime Cure # Catalyst (° C.) (sec) speed 1 DBTDL 100 2600 medium diBuSndilaurate 2 Cu TMHD₂ 100 1600 medium Cu bis-Me₄- heptanedionate 3K682-Bi 100 2000 slow 4 K4205-Zr 120 2700 poor 5 K672-Zn + 100 2300medium Zr 6 ZnF₆AcAc 100 900 good Zn F₆- acetylacetonate 7 K635-Zn 120200 slow

Example 8: 1K formulation stability. Table 6 below shows that fullyformulated cure efficiency and viscosity are retained for 100+ days atambient temperature with triol formulations. By contrast, formulatedamine-cured systems show rapid viscosity rise after 24 hr and becomesolid after a few days.

TABLE 6 Cure Efficiency and Viscosity Vs. Time & Temperature. RPU70 +TPE Tensile Elong. to Resin Triol + 0.25% Ultimate Str @ BreakViscosity, K651 Modulus Tensile Str Yield (mm/mm) # Repeats Pa s green649 17.2 16.7 0.4 5 2.268 4 hr 120° C. 874 27.1 26.1 0.48 5 8 hr 120° C.847 24.4 24.4 0.49 5 plus 18 days 341 12.2 7.95 0.81 5 6.742 @ 40° C.green 4 hr 120° C. 732 23.7 21.1 0.86 5 8 hr 120° C. 784 23.3 21.9 0.795 plus 105 days 731 17.2 17.1 0.55 5 4.705 @ RT green 4 hr 140° C. 90425.7 25.3 0.05 4 8 h 140° C. 1030  29.4 29.4 0.39 5 4 h 160° C. 1000 27.4 27.4 0.41 3

Example 9: Tensile Performance of ABPU Cured with Triamine vs. Triol.Shown in Table 7 below is a comparison of Instron tensile performance ofRPU70 Part A with triamine or triol. The thermally post-cured triolsample shows improvements in modulus, elongation and tensile stress withthermal cure, but modulus is lower than the triamine cured sample, whichmay be due to the reduced hydrogen bonding of urethane linkages vs. theurea linkages in the triamine cured example.

TABLE 7 Modulus Tensile (Auto Tensile stress at Young's, strain Break #RPU70A+ MPa) (mm/mm) (MPa) Repeats T403 triamine 6 hr 1395.4 0.38 29.2 6120 C. TPE triol + 0.5% 595.3 0.51 17.9 4 K651, Green −4 hr 120° C. 8140.63 27.2 5 −2 hr 120° C. + 805 0.54 26.7 5 1 hr 140° C.

Example 10: ABPU Triol Resin Viscosity Stability. Samples of RPU70 PartA formulated with TPE triol and three different catalysts were testedfor viscosity stability after 68 days. K348 (0.25%) and K635 (1%) werestable, but K651 (0.5%) showed a tripling of viscosity. This sample,viscosity 6.74 Pa s, was still printable after 100 days, and asreflected in Table 8 below showed an increase in strength with goodretention of elongation.

TABLE 8 Properties of printed 1K resin after 100 days RPU70 + TPE Ult.Tensile Elong. to Break Triol + 0.5% K651 Str mm/mm Green 12.6 0.61 160°C. 4 hrs 22.5 0.43 140° C. 8 hrs 25.7 0.50

The foregoing is illustrative of the present invention, and is not to beconstrued as limiting thereof. The invention is defined by the followingclaims, with equivalents of the claims to be included therein.

We claim:
 1. A resin product useful for the production ofthree-dimensional objects by additive manufacturing, comprising: (a) areactive blocked prepolymer comprising a prepolymer blocked withreactive blocking groups (e.g., in an amount of from 5 to 90 percent byweight); (b) a polyol (e.g., in an amount of from 5 to 30 or 40 percentby weight); (c) a photoinitiator (e.g., a free radical photoinitiator)(e.g., in an amount of from 0.1 to 4 percent by weight); (d) at leastone organometallic catalyst (e.g., in a total amount of from 0.01, 0.05,0.1, 0.2, or 0.3 percent by weight tol, 2 or 3 percent by weight); (e)optionally, but in some embodiments preferably, a reactive diluent(e.g., in an amount of from 1 or 5 percent by weight to 40 or 50 percentby weight); (f) optionally, but in some embodiments preferably, a filler(e.g., in an amount of from 1, 2, 5 or 10 percent by weight to 50percent by weight); and (g) optionally, but in some embodimentspreferably, a pigment or dye (e.g., in an amount of from 0.05, 0.1 or0.5 percent by weight to 2, 4 or 6 percent by weight).
 2. The resin ofclaim 1, wherein said prepolymer comprises a polyurethane prepolymer, apolyurea prepolymer, a polyurethane-polyurea copolymer, or a combinationthereof.
 3. The resin of claim 1, said reactive blocked prepolymercomprising reactive end groups selected from the group consisting ofacrylates, methacrylates, alpha-olefins, N- vinyls, acrylamides,methacrylamides, styrenics, epoxides, thiols, 1,3-dienes, vinyl halides,acrylonitriles, vinyl esters, maleimides, and vinyl ethers.
 4. The resinof claim 1, wherein said reactive blocking group comprises an amine(meth)acrylate monomer blocking agent (e.g., tertiary-butylaminoethylmethacrylate (TBAEMA), tertiary pentylaminoethyl methacrylate (TPAEMA),tertiary hexylaminoethyl methacrylate (THAEMA),tertiary-butylaminopropyl methacrylate (TBAPMA),tertiary-octylaminoethyl methacrylate (TOAEMA), acrylate analogsthereof, and mixtures thereof).
 5. The resin of claim 1, wherein saidreactive blocked prepolymer comprises a (meth)acrylate-blockedprepolymer.
 6. The resin of claim 1, wherein said reactive blockedprepolymer is blocked with a vinyl amide blocking agent such asN-vinylformamide (NVF) or N-vinylacetamide (NVA).
 7. The resin of claim1, wherein said reactive blocked prepolymer comprises a vinyl amideblocked polyisocyanate.
 8. The resin of claim 7, wherein said vinylamide blocked polyisocyanate comprises an N-vinyl formamide blockedpolyisocyante.
 9. The resin of claim 1, wherein said reactive diluentcomprises an acrylate, a methacrylate, a styrene, a vinylamide, a vinylether, a vinyl ester, polymers containing any one or more of theforegoing, and combinations with one or more of the foregoing (e.g.,acrylonitrile, styrene, divinyl benzene, vinyl toluene, methyl acrylate,ethyl acrylate, butyl acrylate, a fatty alcohol (meth)acrylate such aslauryl acrylate, isobornyl acrylate (IBOA), isobornyl methacrylate(IBOMA), an alkyl ether of mono-, di- or triethylene glycol acrylate ormethacrylate, a fatty alcohol acrylate or methacrylate such as lauryl(meth)acrylate, and mixtures thereof).
 10. The resin of claim 1, whereinsaid polyol is a diol or a triol.
 11. The resin of claim 1, saidorganometallic catalyst comprising: a metal amidine complex and/or asecond compound, wherein the second compound is a metal carboxylate or acarboxylic acid, and/or a third compound wherein the third compound is ametal chelate complex of an acetylacetonate (e.g., pentanedione),optionally wherein the metal of the metal amidine complex and the metalof the metal carboxylate and/or the metal of the metal acetylacetonate(when present) are not identical.
 12. The resin of claim 11, wherein themetal amidine complex is of the chemical formulametal(amidine)_(w)(carboxylate)₂, wherein w is an integer from 1 to 4.13. The resin of claim 11, wherein the metal of the metal amidinecomplex, the metal of the metal carboxylate, and the metal of thechelate complex are independently copper, zinc, lithium, sodium,magnesium, barium, potassium, calcium, bismuth, cadmium, aluminum,zirconium, tin, hafnium, titanium, lanthanum, vanadium, niobium,tantalum, tellurium, molybdenum, tungsten, or cesium.
 14. The resin ofclaim 11, wherein the metal of the metal amidine complex and the metalof the metal carboxylate are independently zinc or bismuth.
 15. Theresin of claim 11, wherein the amidine is 1,1,3,3-tetramethyl guanidineor 1-methylimidazole.
 16. The resin of claim 11, wherein the chelate ispentanedione, hexafluoropentanedione or tetramethyloctanedione.
 17. Theresin of claim 11, wherein the carboxylate is octoate, neodecanoate,naphthenate, stearate, or oxalate.
 18. The resin of claim 11, whereinthe second compound comprises a zinc carboxylate and/or a bismuthcarboxylate.
 19. A packaged product useful for the production ofthree-dimensional objects by additive manufacturing, said productcomprising a single container having a single chamber and a resin in thechamber, the resin comprising a resin of claim 1, with all componentsmixed together (i.e., a “1K resin”).
 20. A method of making athree-dimensional object, comprising: (a) dispensing a resin of claim 1into an additive manufacturing apparatus (e.g., a bottom-up or top-downstereolithography apparatus); (b) producing an intermediate object fromsaid resin by photopolymerization; and then (c) heating and/or microwaveirradiating said intermediate object to further polymerize said resinand form said three-dimensional object.
 21. The method of claim 20,wherein: said producing step (b) is carried out by photopolymerizingsaid reactive blocked prepolymer to form a polymer scaffold carryingsaid polyol; and said heating and/or microwave irradiating step (c) iscarried out under conditions in which said polymer scaffold at leastpartially degrades and regenerates said prepolymer, said prepolymer inturn polymerizing with said polyol to form said three-dimensionalobject.